Department of Cell Genetics, National Institute of Genetics, Yata 1111, Mishima, Shizuoka, 411-8540, Japan.
Department of Genetics, Graduate University for Advanced Studies (SOKENDAI), Mishima, Shizuoka, 411-8540, Japan.
Sci Rep. 2017 May 24;7(1):2345. doi: 10.1038/s41598-017-02668-2.
The chloroplasts of cryptophytes arose through a secondary endosymbiotic event in which a red algal endosymbiont was integrated into a previously nonphotosynthetic eukaryote. The cryptophytes retain a remnant of the endosymbiont nucleus (nucleomorph) that is replicated once in the cell cycle along with the chloroplast. To understand how the chloroplast, nucleomorph and host cell divide in a coordinated manner, we examined the expression of genes/proteins that are related to nucleomorph replication and chloroplast division as well as the timing of nuclear and nucleomorph DNA synthesis in the cryptophyte Guillardia theta. Nucleus-encoded nucleomorph HISTONE H2A mRNA specifically accumulated during the nuclear S phase. In contrast, nucleomorph-encoded genes/proteins that are related to nucleomorph replication and chloroplast division (FtsZ) are constantly expressed throughout the cell cycle. The results of this study and previous studies on chlorarachniophytes suggest that there was a common evolutionary pattern in which an endosymbiont lost its replication cycle-dependent transcription while cell-cycle-dependent transcriptional regulation of host nuclear genes came to restrict the timing of nucleomorph replication and chloroplast division.
隐藻的叶绿体是通过二次内共生事件产生的，其中一个红藻内共生体被整合到一个先前非光合真核生物中。隐藻保留了内共生体核（核质体）的残余物，该核质体在细胞周期中与叶绿体一起复制一次。为了了解叶绿体、核质体和宿主细胞如何协调分裂，我们研究了与核质体复制和叶绿体分裂相关的基因/蛋白质的表达，以及隐藻门 Guilliardia theta 中核和核质体 DNA 合成的时间。核编码的核质体 HISTONE H2A mRNA 在核 S 期特异性积累。相比之下，与核质体复制和叶绿体分裂相关的核质体编码基因/蛋白质（FtsZ）在整个细胞周期中持续表达。本研究和先前对 Chlorarachniophytes 的研究结果表明，存在一种共同的进化模式，即内共生体失去了与其复制周期相关的转录，而宿主核基因的细胞周期依赖性转录调控开始限制核质体复制和叶绿体分裂的时间。
